Dampeb for furnace flues



Dec. s, 1953 W. P. OSGOO D DAMPER FOR FURNACE FLUES Filed Jan. 17, 1950 INVENTOR WALTER P. 056000 3 M ATTYS WIIT Patented Dec. 8, 1953 UNITED STATES PATENT OFFICE DAMPER- I JZZZ'ACE FLUE S 'Walter P. Osgood, 'Malden, Mass., assignor to Boston Machine'= Works Company, Lynn,;Mass.,

a corporation .ofMassachusetts .Application'January'17, 195.0,Serial No. 139.029

' *1 Claim. (ones-45) This invention relates to improvements in furnace flue dampers for automatically regulating the draft in the flue. The proper regulation of draft is an important factor in the combustion of fuel of any kind. since an excessive draft results in an unnecessary and wasteful loss of heat of the chimney. In the case of a heating unit for a building, including an oil burner, it is particularly important that a uniform draft be maintained at the optimum value to ensure proper combustion and minimum heat loss.

Draft in a furnace is due to the maintenance of pressure Within the flue less than theiatmospheric pressure around the furnace. For every given installation, there is generally an optimum pressure diiference for operation of the burner. Thepr sure within the flue, however, is subject tefl-uctuations due to a number of causes'including, for example, variations in the direction and force ofthe wind at the top of the chimney. "To counteract suchfluctuations, it has been customary to provide a damper in the form of a butterfly valve comprising a disc or plate. normally closing anopening through the Wall of theflue at a point ,near its. connection With the furnace, the damperbeing arranged .to swing open about a .diametralaxis in response to small reductions in the pressure within the flue. When thedamper swings open, air is admitted into the flue, thus raising the pressure therein and reducing the z).

draft accordingly. Dampers of this kind are apt to be erratic in operation owing to tendencies to over-compensate or undercompensate for pressure variations in the flue. A number of improved dampers have been designed as, for example, that shown in thepatent to Cunningham. No. 2,251,440, granted August 5, 1941. According to the present invention, certain improvements are added to a damper of the type shown, in said patent for the purpose of making the operation of the damper more reliable and effective ininstallations having widely different requirements of draft, as hereinafter set forth'in detail.

For a more complete understanding of the invention, reference may be had to the following description thereof, and to the drawing, of which Figure 1 is a plan view of a conventional installation of a damper embodying the invention;

Figure 2 is a section on the line 22 of Figure 1, showing a rear View of the damper;

Figure 3 is a section on the line 3-3 of Figure 2; and

Figure 4 is a section on the line 3-4 of Figure 2.

As indicated in Figure 1, a customary way of installinga damper is to mount it On a short piece of smoke pipe 10 wl'iich'opens into the side of a flue l2 such'as is used to connect a furnace to a chimney. The damper may comprise a circular frame l4 adaptedto fit into the open end of the pipe l0 and to lee-secured inplace' by two or'mcre set screwslfi. A disc-2D is fitted within the opening of the circular frame it and is pivotally mounted therein so as to rock about a diametral axis. For'this purpose'the frame id may be provioled with a pair of bearing screws '22 which are diametrically opposed to each other and which have point bearings 24 entering sockets in the'ends of a pair of short rods 26 which are secured to the disc 29. In order to hold the rods 26 in place, they-may be clamped against the rear face of the circular disc 26 by a plate as which is secured to the rear face of the disc by spot welding or other suitable means, this plate beingin the-form of a central zone of a circle the size of the disc 28,-the end edges of the plate 23 coinciding for-the most partwith arcuate edge portions of the disc'ZB. "The side margins of the plate 36 are'bent' up perpendicular to the body of the plate to former pair of transverse ribs orflns and 3d whichare chords of the circle of the disc and-are parallel to the rocking axis. The plate 39 is previded with a pair of notches 33 at each end so that the metalbetwcen the-notches can be arched upward as at 3'8 to receive the rods 26 between the arches and the disc 21!, as indicated in Figures 2 and 4. "The notches '36 permit'the arching ofthe metal between them without distorting the plate 30 as a whole or causing cracks therein. The damper may be mounted with its resizing aria; horizontal, but it is usually preferably to'mount it with its axis-inclined-at an angle of about 30 degrees to'thehorizontal, as illustrated in Figure 2.

The circular'frame Mis made with a segmentshaped partition 33 within the upper portion thereof, this partition being spaced behind the upper'portiono-fthedisc 2E! and having a flange 42 to form a shallow chamber 44. A suitable hole 46 is provided in the disc to open into the chamber 44 and thus to admit air from the atmosphere into the chamber. Some air also enters the chamber through the narrow space along the edge of the disc, but this is usually insufficient to avoid an air-lock resulting in a reduction in the sensitivity of the damper to small reductions of pressure in the flue. When the disc is in its closed position, shown in Figure 3, it virtually closes the pipe l0. Since the rocking axis of the disc is diametral, the aerostatic pressure on the upper and lower halves of the front face of the disc is substantially balanced. The pressure within the pipe iii which acts against the rear face of the disc is unbalanced owing to the presence of the partition til which partially cuts off the uppermost portion of the disc from aerostatic pressure within the pipe it. The hole 45 admits atmospheric air to enter the chamber td and since the atmospheric air pressure is always greater than the flue pressure the pressure within the chamber M is generally greater against the upper portion of the disc than is the flue pressure against the lower portion of the disc. Thus there is an unbalance tending to swing the disc in a clockwise direction from the closed position as shown in Figure 3.

In order to prevent opening of the disc prematurely or at flue pressures higher than the pressure required for the desired degree of draft, a counterweight 52* is provided. This counterweight is adiustably mounted on a bracket 52 which, as indicated in the figures of the drawing, may be a strip of. metal secured at one end to the rear face of the damper at a point above the rocking axis, this bracket member projecting away from the plane of the disc at a skew angle and extending downward so that the opposite end is well below the rocking axis. As is evident from Figure 2, the projection of the bracket member 52 upon the plane of the disc intersects the rocking axis at a point at or near the center of the disc and makes with this axis an oblique angle. The counterweight 5% may be adjustably fixed at any point along the bracket 52 to provide for any desired degree of draft within the range of the device. Thus for low drafts, the counterweight will be secured in a position near the upper end of the bracket, that is, the end at which the bracket is attached to the disc. Owing to the location of the bracket and the shape of the counterweight, when the counterweight is adjusted to give minimum draft, it is in direct contact with the face of the plate as slightly below the rocking axis of the disc 28 and is thus approximately tangent to the rocking axis as is evident from Figure 4.- When in this position of adjustment, a portion of the counterweight is above the rocking axis. For higher drafts, the counterweight will be secured further down the bracket, that is, nearer the free end thereof.

After the damper has been suitably installe and adjusted to regulate the draft within the flue to the desired magnitude, a decrease of pressure within the flue which would result in an excessive draft causes the disc 2i! to swing open sufilciently to correct the situation by admitting suiiicient air to raise the flue pressure to a point where the desired draft is obtained. The end 5 of the bracket 52 is arranged to act as a stop to limit the rocking movement of the disc to an arc of ninety degrees. When the disc is thus rocked to open the damper fully, the stop ele- '4 ment 54 strikes a cushion member 56 which may conveniently be in the form of the head of a soft rubber peg 58. This peg is inserted through a hole in the partition 40 and extends forward far enough to act as a resilient stop against which the disc itself strikes when it returns to its closed position as shown in Figure 3. The shank of the rubber peg 58 is slightly greater than the hole through which it extends. By pulling the shank so that it stretches when it is being inserted in the hole, it is thus reduced in diameter so that it can move through the hole until the head engages the rear face of the partition 40. Release of the shank 58 permits it to expand so that it fits tightly within the hole.

The attachment of the bracket member 52 to the rear face of the disc at a point above the rocking axis has the effect of making the damper capable of operating effectively when installed to regulate either drafts of relatively high degree or of relatively low degree. In this respect the bracket member 52 is superior to a bracket which projects out radially from the axis of the disc. In the latter case, the damper is not as effective in maintaining a constant draft of relatively low degree,

The bracket member 52, may, if desired, be made with scale marks and indicia showing the positions in which the counterweight should be secured in order to maintain drafts of certain predetermined magnitudes within the form. In general, when the damper has once been adjusted in a given installation, no further adjustment will be required unless a different degree of draft is later desired for some such reason as a change in the fuel used in the furnace.

I claim:

A damper for a furnace flue comprising a circular frame a disc fitted therein in a normally vertical plane and pivotally mounted to rock about a diametral axis, a segment-shaped partition mounted within said frame behind the upper portion of said disc to form with said upper portion a shallow chamber, a bracket member projecting at a skew angle from the rear face of said, disc, a counterweight mounted on said bracket, and a resilient stop element extending through said partition and engaged by said disc when the disc is in its normal position and by said bracket member when the disc is at right angles to its normal position.

WALTER P. OSGOOD.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,263,830 Wolf Apr. 23, 1918 1,943,342 Mortimer Jan. 16, 1934 1,945,955 Price Feb. 6, 1934 2,251,440 Cunningham Aug. 5, 1941 2,285,746 Sabins June 9, 1942 2,346,825 Cole Apr. 18, 1944 

